Emitters with small tip diameters (e.g., 100 nm or less) used for electron emission are affected by vacuum conditions. The vacuum conditions can deteriorate field emission performance. Typical electron emitters do not have protective coating to protect from oxidation or carbon build up. A carbon layer grows on the surface of the cathode tips during electron beam emission under ultra-high vacuum (UHV) conditions. Oxidation of surfaces in UHV environments is also likely. Previous designs were not robust to cleaning of, for example, oxidation or carbon layers. Molecules from the vacuum (e.g., hydrogen, carbon monoxide, oxygen, nitrogen, and water) also can adsorb onto the cathode tip, and this can lead to a drop in the field emission current and instability in the field emission current.
Silicon is a good candidate material for making nanotips to be used as electron emitters because of well-established silicon microfabrication techniques. However, silicon emitters are highly susceptibility to oxidation, which converts the emitter tip to a silicon oxide. The silicon oxide will render the tip inoperable for electron emission due to the high work function of the silicon oxide. Stability also is affected by presence of silicon oxide on the emitter. There is no clear method to prevent this from occurring over the system lifetime.
Therefore, what is needed is an improved electron emitter and methods of operation.